Cannot draw my model twice in OpenGL? - c++

Question

I want to draw a model of a chair that I exported from 3ds max as a txt file. I read the file and display it in OpenGL (using Visual Studio -> C++). My problem is that I have to multiplicate the chair many times (10). I did try to multiplicate it twice but it does not work. The program crashes with these "Program is not responding" Windows errors. I have a main class that calls all of the nessessery methods from CDrawModel like that:
CDrawModel mModel;
int main(int argc, char **argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB);
glutInitWindowSize( 1000, 600 );
glutInitWindowPosition(100, 100);
glutCreateWindow("Georgi Koemdzhiev - 1306794");
glutKeyboardFunc(KeyResponse);
glutDisplayFunc(DrawGLScene);
glutReshapeFunc(ReSizeGLScene);
mModel.initGL();
glutMainLoop();
}
void DrawGLScene(void) {
mModel.myDrawGLScene();
}
GLvoid ReSizeGLScene(GLsizei fwidth, GLsizei fheight) {
mModel.MyReSizeGLScene(fwidth, fheight);
}
CDrawModal initialises an object of type CPolygonMesh which handles the reading from the file and drawing on the screen functionality. I know my code works since I am getting my modal drawn on the screen:
this is my CDrawModal class:
oid CDrawModel::initGL(void) {
glClearColor(1.0, 1.0, 1.0, 1.0);
near = 1.0;
far = 1000.0;
height = 1.5;
glCullFace(GL_BACK); // don’t draw back facing faces
glEnable(GL_CULL_FACE); // enable face culling
glPolygonMode(GL_FRONT, GL_LINE); // select front polygons and draw edges only
}
void CDrawModel::MyReSizeGLScene(int fwidth, int fheight) // Resize And Initialize The GL Window{
// Store window size so it can be accessed in myDrawGLScene()
wWidth = fwidth;
wHeight = fheight;
// Set fovy so that the viewing frustum has the specified height at the
// near clipping plane
fovy = (360 / PI) * atan(height / (2.0 * near));
// Calculate the aspect ratio of the VIEWPORT
// so that we can set the camera’s aspect ratio to the same value
aspect_ratio = (double)fwidth / (double)fheight;
glMatrixMode(GL_PROJECTION); // Select The Projection Stack
glLoadIdentity();
/* void glOrtho( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble nearVal,
GLdouble farVal);*/
gluPerspective(90, aspect_ratio, near, far); // perspective view
//glOrtho(-130.0,130.0,-130.0,130.0,near,far);
glViewport(0, 0, wWidth, wHeight); // Viewport fills the window
// Print values of parameters
cout << fixed; // Use fixed-point notation
cout.precision(3); // Number of digits after the decimal point
cout << "fovy = " << fovy << endl;
cout << "aspect_ratio = " << aspect_ratio << endl;
cout << "near = " << near << endl;
cout << "far = " << far << endl;
}
void CDrawModel::myDrawGLScene(GLvoid) // Here's Where We Do All The Drawing
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // clear the drawing area
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0, -200);
mesh.draw_model();
glutSwapBuffers(); // Needed if we're running an animation
glFlush();
}
What I need to do in order to draw it twice.This is my drawModal method in CPolugonMesh:
void CPolygonMesh::draw_model(void){
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glColor3f(1.0, 0.0, 0.0); // draw red things
glBegin(GL_TRIANGLES);
for (int i = 0; i < Mesh_NumFaces; i++) {
// Look up the coordinates of each vertex
// in vertex_list[]
glVertex3fv(vertex_list[ face_list[i][0] ]);
glVertex3fv(vertex_list[ face_list[i][1] ]);
glVertex3fv(vertex_list[ face_list[i][2] ]);
//cout << "Drawing face: " << i << endl;
}
glEnd();
}

Answer 1

Your CPolygonMesh::draw_model(void) method actually clears the screen each time you draw a model, so only the last call will leave anything on the screen.
The line
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
is totally wrong there. You already do clear the screen at the beginning of your frame.